A negative glow lamp typically is comprised of a light-transmitting envelope containing a noble gas and mercury with a phosphor coating on an inner surface of the envelope which is adapted to emit visible light upon absorption of ultraviolet radiation that occurs when the lamp is excited. The lamp is excited by means of the application of a voltage between the lamp electrodes. Current flows between the electrodes after a certain potential is applied to the electrodes, commonly referred to as the breakdown voltage. An elementary explanation of the phenomenon is that the gas between the electrodes becomes ionized at a certain voltage, conducts current, and emits ultraviolet radiation. The phosphor coating on the inner surface of the lamp envelope is caused to fluoresce and re-emit a substantial portion of the ultraviolet radiation as visible light. The spectral characteristics of the visible light is determined by the composition of the fluorescent powders used for the phosphor coating.
Examples of typical glow discharge lamps are found in U.S. Pat. No. 2,341,990 to Inman et al and U.S. Pat. No. 2,403,184 to Lemmers.
It is important that the anode electrode of the glow discharge lamp have a large enough surface to prevent a positive anode voltage drop (PAVD). At the same time, the anode has to be small enough to be transparent for ultraviolet and visible radiation. Both of these considerably affect the lamp efficiency. The PAVD appears around the anode when electron diffusion to the anode can not compensate the electron sink to the anode which corresponds to the discharge current. The development of a PAVD in discharges operating in a dc regime leads to useless anode heating and consequently to unnecessary electric power losses.
In a typical negative glow discharge lamp operating in a dc regime, the anode is in the form of a rectangular plate which is positioned normal to the cathode direction. The rectangularly-shaped anode plate is 2.0 centimeters by centimeter and is placed 1.0-2.0 centimeters from the cathode. This configuration results in only one side of the anode plate facing the cathode. As a result, the opposite side of the anode plate seldom takes part in electron collection because of the screening effect. Plasma density on this opposite side is much smaller than that on the side facing the cathode. Accordingly, the anode has the collection surface close to the screening light surface. Moreover, plasma density around this anode should be considerably depleted which results in a positive anode voltage drop.